<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        'use strict';
        // 默认是全局变量
        let i;
        i=1;
        // es6中局部变量用let定义
    </script>
</head>
<body>

</body>
</html>